Tilt rotor aircraft represent an innovative step in the evolution of aircraft design. The tilt rotor design allows an aircraft to assume the vertical take-off and landing characteristics of a helicopter. Once in flight, the rotors can rotate forward, allowing the aircraft to fly like a fixed wing aircraft. To minimize the weight of the vehicle a shorter stiffer wing is used. This leaves little space for effective control surfaces.
A typical wing design for an aircraft includes a primary wing surface incorporating ailerons and flaps. The flaps are designed to increase wing lift while the ailerons are used for roll axis control. The flaps on each wing operate in unison to increase wing lift by increasing the camber of the wing. By comparison, ailerons are pivoted oppositely to increase lift on one wing while reducing lift on the opposite wing to induce a rolling moment.
Due to the marginal space available on the wing area of tilt rotor aircraft, in some designs the flaps and ailerons have been combined into a single unit known as the flaperon. In most designs at least one flaperon unit is located on each wing of the aircraft. On take-offs or landings, the flaperons work in conjunction to provide additional wing lift. To induce aircraft roll, the flaperons are pivoted in opposite directions to effect such a manuever.
Aerodynamic lift of a tilt rotor wing is dependent on, among other things, the deflection of the flaperon, the size of the wing, the flight speed of the vehicle, and the state of the air that is flowing over the surface of the wing. To effectively produce lift, the air must flow smoothly over the wing without producing flow separation and the associated large regions of dead air. Large regions of flow separation are associated with stall of the wing and small regions of flow separation increase drag. At low speed flight conditions, downward rotations of the flaperon are required to minimize flow separation and generate the necessary lift force. As the speed of the vehicle is increased, the lift force is increased due to increased dynamic pressure and less flap downward rotation is needed to generate the required lift force.
At these high-speed airplane cruise conditions, large amounts of drag force will be generated, due to flow separation, if the gap between the trailing edge of the wing and the flaperon remains open. Since the flaperon must also rotate upward in the high speed forward condition to provide roll control, flow characteristics over this gap can be improved by a device which will bridge the gap and provide a continuous flow surface.
Several devices have been built to augment the lift capability of different types of flight vehicles. For example, U.S. Pat. No. 3,977,630 to Lewis et al., discloses a wing design for a Short Take-off and Landing (STOL) aircraft. The design incorporates a multi-segmented externally-blown flap that uses jet exhaust to augment the lift, and more notably slot closing devices. When the flap pieces extend from each other, slot closing devices, which are controlled independently of the position of the flaps, bridge the spanwise slots or coves formed by the extended flaps.
U.S. Pat. No. 3,112,089 to Dornier discloses a segmented flap. The segments are shaped such that when the flap is lowered the segments rotate to produce a substantially continuous top surface. This design fails to provide a separate gap control device.
U.S. Pat. No. 2,772,058 to Grant discloses a slot controller. This slot controller helps fill the gap between the trailing edge of the wing and the primary flap assembly at only certain flap orientations. As the flaps are rotated upwardly, they act as spoilers and a gap is opened between the flap and wing section.
U.S. Pat. No. 3,223,356 to Alverez-Calderon discloses a wing flap system for a Vertical Take-off and Landing (VTOL) aircraft that includes a rotating cylinder and a cover plate for providing a low drag surface between the upper surface of the wing and associated flap. The flap system has movable portions including inboard and outboard regions. These regions are deflected at a fixed negative flap setting for cruise. However, the flaps cannot move during cruise.
U.S. Pat. No. 2,908,454 to DeWolff is to one aircraft wing having multiple flaps driven by a track linkage for controlling the downward motion of the flaps. The system does not provide for a flaperon combination with structure for controlling the gap between the flaperon and wing at all flaperon orientations.
A need exists for a device that will function as both the flaps and the ailerons with an appropriate seal for bridging and thereby selectively sealing the gap between the primary wing surface and the flaperon at appropriate flaperon orientations. Such a seal should provide an uninterrupted upper boundary wing surface to eliminate drag due to flow moving from the lower surface to the upper surface. Additionally, a system is needed for controlling the angular orientation of this flaperon seal so that it is easily, and automatically positioned properly for all angles of adjustment relative to the wing segment.